The present invention relates to a paper currency recognition system for use in a money exchange machine and, more particularly, to a paper currency recognition system which automatically regulates the LED driving voltage and the signal or induction current of a phototransistor so that the intensity of light of the transmitter is constantly maintained within a constant value, and the induction current of the receiver is constantly maintained within a readable range.
A money exchange machine has a paper currency recognition system adapted for recognizing the authenticity of the inserted paper currency. The paper currency recognition system is installed in a transferring mechanism downstream of the currency insertion slot. When paper currency is inserted through the currency insertion slot into the transferring mechanism, a transmitter unit of the paper currency recognition system emits a light onto the inserted paper currency, and a receiver unit of the paper currency recognition system receives the light reflected from the inserted paper currency. When the reflected light is received from the inserted paper currency, the receiver unit produces a signal current readable by a CPU of the paper currency recognition system for recognizing the authenticity of the inserted paper currency. The transmitter unit of the paper currency recognition system uses an LED (light emitting diode) as the light source. The receiver unit of the paper currency recognition system uses a phototransistor to produce the signal current from the light reflected from the inserted paper currency. This design of a paper currency recognition system is still not satisfactory in function because the LED attenuates with use. After a long use, the intensity of light of the LED becomes relatively reduced, resulting in a recognition error.
The present invention provides a paper currency recognition system which eliminates the aforesaid problem. According to the present invention, the paper currency recognition system is used in a money exchange machine and is adapted to recognize the authenticity of paper currency that has been inserted into the money exchange machine, and comprises a transmitter unit, a receiver unit, and a CPU (central processing unit) controlling the operation of the transmitter unit and the receiver unit. The transmitter unit comprises a LED (light emitting diode) adapted for emitting light onto paper currency that has been inserted into the money exchange machine, and a control chip adapted for providing a driving current to drive the LED. The receiver unit comprises a phototransistor, which produces an induction or signal current from the light emitted from the LED and reflected by the paper currency, and an N-channel MOSFET (metal-oxide-semiconductor field effect transistor). When a variation of the signal current from the receiver unit is detected, the CPU controls the MOSFET to let a part of the induction current be shunt to the MOSFET, enabling the value of the induction current to be regulated to a readable range, and at the same time drives a control chip to regulate the LED driving current, keeping the light intensity of the LED to be maintained within a constant value.